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Plant adaptation to a changing environment

Postdoc-stipendium i Danmark | 21/12/16

Photo by Elizabeth H. J. Neilson.

As sessile organisms, plants must possess mechanisms to tolerate a wide range of abiotic and biotic stresses throughout their lifetime. In order to cope under the constant pressure of herbivory and pathogen attach as well as challenging environmental conditions and even catastrophic events, plants must be plastic to survive. Survival is particularly impressive in long-lived tree species, where individuals must tolerate biotic pressures and changes in their environment over many centuries.

Specialized metabolites play an important role in plant protection against biotic and abiotic stress. As a general trend, specialized metabolites increase in concentration when plants are subject to abiotic stresses such as extreme temperatures, drought and changes in atmospheric conditions. In today’s climate, where temperatures and CO2 concentrations are increasing at unprecedented rates, it remains largely unknown to what degree plants will adapt and change their chemical composition, and ultimately how these changes will affect plant-animal interactions and the flow-on effect through the food chain.

Long-lived eucalypt trees, chemical diversity and their ability to survive

"Southern hemisphere forests have rarely been investigated in the context of defence chemistry and climate change, despite the increasing importance and prevalence of plantation forests of genera such as Eucalyptus throughout the world” 
- Goodger and Woodrow 2013, Trees in a Changing Environment, Plant Ecophysiology

The Australian genus Eucalyptus consists of fast growing, long-lived trees (up to 500 years), and dominate a vast array of climatic regions: from arid and semi-arid environments, to alpine regions, waterlogged swamps and temperate rainforests (Box 1). As such, eucalypts provides an excellent system to investigate tree plasticity and survival across different environmental conditions.

The success of eucalypt trees can be attributed, in part, to their ability to produce a wide range of specialized metabolites, including terpenoids, phenolics and cyanogenic glucosides. Distinct differences are widely observed across the genus. For example, E. camphora groups into two distinct chemotypes: southern E. camphora trees produce the phenylalanine-derived cyanogenic glucoside prunasin with the monoterpene 1,8-cineole as the major terpenoid constituent. Northern trees are acyanogenic and characterized by the presence of the sesquiterpenes α-, β-, and ƴ-eudesmol (Box 1).

Box 1. Physical and chemical diversity and variation in Eucalyptus species

Variation in eucalypt volatile emissions

Many specialized metabolites can be volatilized, such that a complex chemical blend of metabolites is emitted from the plant tissue enabling communication with other plants and organisms in response to biotic stress. Volatile compounds also play a fundamental role in plant reproductive success, whereby volatile compounds are used to attract appropriate pollinators and fruit dispersers, whilst concurrently detering florivores, frugivores and nectar-robbers. Despite the high degree of variation in eucalypt flower size, nectar composition, and colour (Fig 1C), eucalypt flower and leaf volatiles have virtually remained unexplored. 

In collaboration with Associate Professor Riikka Rinnan, we have undertaken the first in-depth screen of eucalypt leaf and flower volatile emissions in the under field conditions in southern Australia (see Box 2). Distinct emission patterns within and between eucalypt species are observed, with different species emitting a distinct scent from their leaves and flowers; the volatile profile emitted changes diurnally. This information is now being used as a basis to investigate how eucalypt emissions will change under altered environmental conditions (such as increased temperatures and elevated atmospheric CO2) to understand potential impacts on other organisms such as herbivores and pollinators.

Box 2. Measuring chemical and physical properties of eucalypts

Will atmospheric and climatic changes impact eucalypt chemistry and their herbivores?

”Within the next few decades, many eucalypt species will have their entire present-day populations exposed to temperatures and rainfalls under which no individuals currently exist” - Hughes et al 1996, Global Ecology and Biogeography Letters 5:128-142

Despite being highly toxic and poorly nutritious, eucalypts are the sole food of the iconic koala (Phascolarctos cinereus). The ability of the koala to survive on a eucalypt diet is the result of a finely tuned energy budget between the koala, its gut microbe community and the chemical composition of the eucalypt leaves. Climate change threatens this fine balance due to a hypothesised increase in specialized metabolite concentrations and decrease in available protein. Therefore, if climate change is affecting the chemistry of eucalypt leaves, the fine balance between nutritional intake vs metabolite detoxification in the koala will be disrupted (See Box 3).

Box. 3 Will atmospheric and climatic changes affect wildlife systems?

Ongoing and future work will investigate the mechanisms by which eucalypts synthesize selected classes of chemical toxins and examine how the regulation of these metabolites changes in response to increasing temperature and atmospheric CO2 concentration.  Specifically, this project will measure the changes in eucalypt chemistry at the molecular, tissue and whole plant level. Furthermore, this project will examine how climatic factors may disrupt the energy balance between available nutrition and leaf toxicity.  The koala is an internationally iconic animal, so linking findings from this project to koala health and survival rates can quickly bring universal public awareness to the global issue of climate change.

Financial support of fundamental biology and early career scientists is invaluable

“The Carlsberg Foundation grant I received to support basic research is invaluable. From a scientific perspective, the results I have generated are highly relevant and have been applied to other plant species, including important crop plants. From a personal perspective, the Carlsberg Foundation has enabled me to pursue science that excites me and supports my development as an early-career scientist.”

Previous work revealed that Eucalyptus camphora synthesized novel cyanogenic diglucosides, hypothesized to be involved in other metabolic functions in addition to chemical defense (Neilson et al 2011). This knowledge led to the identification of new and additional turnover compounds in the agriculturally important almond tree, cassava, almond and sorghum (Pičmanová et al 2015). Understanding the role of these turnover metabolites is essential, as it is becoming more apparent that specialized metabolites are involved in primary plant metabolism such as the storage and recycling of nitrogen. To determine their role, metabolite localization studies via state-of-the-art MALDI-MS imaging are currently being undertaken. In addition, plant growth and performance is being assessed with the latest technology in plant phenomics, whereby plants are imaged and assessed in a high-throughput, non-destructive manner (Neilson et al. 2015).

Peer-reviewed papers

Neilson EH, Edwards A, Berger B, Blomstedt CK, Møller BL, Gleadow RM (2015) "Utilisation of a high-throughput shoot imaging system to examine the dynamic phenotypic response of a C4 cereal subject to nutrient and water deficiency over time". Journal of Experimental Botany 66: 1817-1832

Pičmanová M, Neilson EH, Motawia MS, Olsen CE, Agerbirk N, Gray CJ, Flitsch S, Meier S, Silvestro D, Jørgensen K, Sánchez-Pérez R, Møller BL, Bjarnholt N (2015) "A recycling pathway for cyanogenic glycosides evidenced by the comparative metabolic profiling in three cyanogenic plant species". Biochemical Journal 469: 375-389

Other relevant papers